Input Bias Current in an OP-AMP and its value in a datasheet

Question

Yes,i have seen all those similar questions of this topic and I am still confused about few concepts.So far i have been taught that an simplified OP-AMP circuit looks like this--------------

So,thinking about input bias current in that circuit here are some confusions-------

1)In a Youtube video i was told that input bias current enters/leaves from both inverting and non-inverting terminal at the same time...and they are equal,How?

2)In an OP-AMP datasheet we have only one value of Input bias current----

But what if the source voltage changes along with the source resistance in that term the bias current also has to change(Below is my note,about what i mean to say)-----

So,we should have different values of input bias current but why only 1 value of input bias current is given in the datasheet?

Answer 1

Bias current is the typical/max current that can be assumed to flow at both input terminals.

Offset current is the typical/max difference in the bias currents.

When multiplied by any series resistor on inputs, bias current gives you the typical/max voltage that each input might settle to due to its bias current.

If an opamp has a large resistor between output and -ve input, and the same value resistor from ground to +ve input to compensate, then the offset current times that resistor value gives you the typical/max output voltage to expect from the imbalance in bias currents.